Automatic control system for rolling mills and adjustable dies



Feb. 18, 1964` E. A. WEREMEYCHIK ETAL AUTOMATIC CONTROL SYSTEM FORROLLING MILLS AND ADJUSTABLE DIES 2 Sheets-Sheet 1 Filed April '7, 1961Feb. 18. 1964 E. A. WEREMEYCHIK ETAL 3,121,354

AUTOMATIC CONTROL SYSTEM FOR ROLLING MILLS AND ADJUSTABLE DIES 2Sheets-Sheet 2 Filed April 7, 1961 Jomes B.Murt|Ond,Jr. EugeneA.Weremeychk BY@ B77 M ATTO R NEY UnitedStates Patent O Filed Apr. 7,1961, Ser. No. 101,535 S Claims. (Cl. 80-56) This invention relates tothe production of material by rolling through 4single or multiple standrolling mills or by drawing through single or multiple ldies of thelcind having opposed die surfaces whose separation is adjustable. Moreparticularly, the invention relates to an automatic system forcontrolling such mills or dies so as to produce material iof 'apredetermined desired uniform gage thickness.

ln the majority of existing control systems for mills and dies, `a millscreWdoWn or the like is controlled from a gage measurement takenseveral feet beyond the exit lside `of the mill, by an elongation orpercent reduction measurement, or by a roll pressure measurement. In asystem employing `a gage measurement, the material, after reduction,progresses to the gage which may be several feet beyond the bite of themill before yany error presen-t in the material thickness can bedetected. This distance from the bite of the rolls to the gage iscommonly referred to yas transport distance. The time required tor thematerial to reach the exi-t gage is denoted yas transport time, Whilethe time required to measure the strip gage is referred to as sensingtime. Transport time and sensing time are major elements in developingerror comin-ands. Transport distances of tive feet or more `are commonin most of the commercial rolling equipment yavailable at present,meaning that such a system would not be capable of detecting an errorsignal until live feet of material had passed from the bite off the millrolls. The `corrective signal would then be transmitted to the millscrewdown; ybut the measuring gage would not `detect the result of thisaction until live feet more of the material had passed through the mill.With a high gain system of this type, la natural frequency ofoscillation results; and if this oscillation is left to exist withoutany Aattempt to control it, the results would be undesirable. That is,for `a material entering the mill With fairly noticeable changes ingage, the system described would cause wide variations in output gagethat in tall probability would eventually result in tearing of thestrip. In an attempt to control the natural frequency of oscillation,some designers have damped their system so y as -to -allow only lacer-tain portion of the requested corrective signal after eachmeasurement to be transmitted to the screwdown. Other designers haveprovided damping in the screws in order to slow Edown the response toany corrective sign-als. yIn `any event, damping considerably reducesthe efciency and effectiveness of the control system. In a highly dampedsystem, the result .is a number of ensuing measurements before thematerial is brought within gage limits resulting in wasted materialWhich has progressed from the mill before the desired gage can beobtained. In present day commercial mills, this loss is considerable.

A system employing `elongation measurements las a means of control hasone basic advantage-the transport distance of such a system is zero thestrip is under tension. in such a system length measuring devices arepositioned at the entrance and exit ends of the mill. For a certainincrement of length passing through the entering length measuringdevice, there Will be an equal or greater increment of length measuredat the exit device, this exit length being dependent upon the reduction`effected by the 3,121,354 Patented Feb. 18, 19.64

ice

mill. Since the transport time with the strip in tension is Zero, theonly time delay in the system will be the time involved in sensingsample lengths ait the entrance and exit of the mill. These 4incrementscan be made so short las to be ignored. Although it would appear that anelongation type of system control would be desirable, further analysisshows a serious shortcoming of this system. An elongation system willonly reduce the material a given percentage. Furthermore, this systemdoes not control toa given gage unless the entering strip gage isconstant. Since the gage of the entering strip varies, this type ofcontrol is an inaccurate means of gage control. To illustrate, let us`assume that an increment of material 0.040 inch thick enters the millfollowed by an increment 0.080 inch thick. It is further supposed thatthe :opening between the mill rolls is such as to reduce the firstincrement to `a thickness or gage of 0.020 inch. In idoing so, the`material must then have been elongated to twice its original length.When the second increment of material (0.080 inch thick) enters themill, it will also `be reduced to `a gage of 0.020 inch. However, theelongation in this case is four times the original length; therefore,corrective mill action will be requested by the system in the secondcase. However, corrective mill action is not `desired since the enitgage or thickness is in both cases alike. Thus, it can be seen that asystem employing elongation measuring methods `alone is not feasible forgage control.

Systems utilizing roll pressure measurements las a means of controlleave much to be desired when precision control of strip gage isrequired. First, an inherent facytor in `a pressure measuring system isthe natural spring of the mill housing. There is no reasonable means ofkeeping the mill housing rigid under the extreme forces encountered inrolling. Compensating for this housing lspring is possible; however, asecond disadvantage still exists in a roll ypressure measuring system.This appears as a result of differences in material hardness iatdifferent points in a strip. That is, hard materials will not be reducedas much as soft materials under certain roll pressure conditions.

The present invention is an outgrowth of a recently vdeveloped method`for rolling mill control based on the concept that the volume ofmaterial coming out :of the mill must be equal to the volume enteringthe mill. With this system, the transport time is zero `and themeasuring time is essentially zero also, meaning that .the systemmeasures `and controls the mill or other similar device directly `at thebite of the mill. Thus:

V1: V2 and (1) L1W1G1=L2W2G2 where L1=length of material entering themill; L2=length of material leaving the mill; G1=g`age off materialentering ythe mill; G2=gage of material leaving the mill; Wlzwidth iofmaterial entering the mill; and Wzzwidth of material leaving the mill.

Previous to this invention, rolling mill control systems based on theconstant volume principle derived an error signal for the rolling millscrewdown by calculating the desired input gage (El) yfrom the othervariables of L1, W1, L2, W2 and G2 and then comparing this calculateddesired input gage against the yactual measured value of input gage G1.Equation-Wise, this may be written:

As will be understood, the output gage of the strip or other workpieceis the factor to be controlled by the system. Therefore, predetermineddesired output gage Gzd is introduced into the system which alters theforegoing equation as follows:

At the same time, the use of desired output gage Gzd rather than actualoutput gage G2 renders the `system capable of control before the factrather than after the fact. In other words, the system will not need toWait until the material has progressed beyond the bite of the millbefore recognizing and deciding on the necessary control operation.

Furthermore, such prior art systems operated on the assumption that theinput width W1 varied from the output width W2 by a constant errorfactor. This factor was represented as W and introduced into theequation as follows:

The equation wlas then complete except for a second error factor K whichwas introduced to take care of any deviations in the dimensions of thegages employed to measure the factors L1 and L2. Thus, the equationbecame:

Although a system based upon the foregoing equation will operatesatisfactorily for its intended purpose, the factors W and K greatlycomplicate the electrical computer circuitry required to compute thefactor Error: G1- G1 G1 Specically, the computation of WXK requires aconsiderable amount of time as well as a great deal of complicatedcomputer circuitry.

As an overall object, the present invention seeks to provide a new andimproved automatic control system for rolling mills `or systemsemploying adjustable dies which measures gage and controls the mill ordies at the bite of the mill.

More specifically, an object of the invention is to provide an automaticcontrol system of the type described which is greatly simplified overprevious constant volume control systems in that it eliminates thefactors W and K discussed above and the attendant computer circuitryrequired to introduce these factors into the error signal equation.

Still another object of the invention is to provide an automatic controlsystem for rolling mills and the like which is greatly simpliiied overprevious systems in that it eliminates many of the circuit components,over and above those required to introduce the aforesaid W and K factorsintoV the error equation, which were heretofore believed necessary forthe successful operation of a rolling mill control system of this typeto obtain a uniform output gage.

Among other things, the present invention resides in the discovery thatcontrary to what is expected, the W and K factors may be eliminated fromthe rolling mill control system, notwithstanding the f-act that theentire system is based upon the premise that the volume of materialentering the mill is equal to that leaving the mill. Thus, although asystem of this sort would logically require that the width of the stripentering and leaving the mill be taken into consideration as a separatefactor, it has been found that variations in width as well as variationsin gage rolls and other variables i may be eliminated withoutsacrificing the desired result which is an output strip of constant anduniform gage. This not only simplifies they computation of the errorequation, but also greatly decreases the amount of circuitry required toeffect the desired result.

In accordance with another aspect of the invention, much of theequipment heretofore believed necessary in a constant volume controlsystem has been eliminated. For example, it is necessary in a gagecontrol system based on the constant volume principle to advance entrygage measurements through an entry gage storage unit in synchronism withthe movement of strip material. In the past, it Was believed necessaryto clear this storage unit of previously stored entry gage informationbefore initiating gage measurements on a succeeding strip. This,however, is unnecessary since, although the gage measurements will beerroneous until the strip has tnavelled a distance sufficient to clearthe storage unit, this amount of strip travel is only a small incrementof the total strip length and can be scrapped if necessary. At the sametime, the complicated circuitry required to clear the storage unit iscompletely eliminated from the control system.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings which form a part of this specification,and in which:

FIGURES 1a and lb form a composite overall schematic and block diagramof the gage control system of the invention; and

FIG. 2 is an illustration of wave forms appearing at various points inthe circuit of FIGS. 1a and 1b.

Referring now to the drawings, `and particularly to FIGS. 1a and 1b, aconventional rolling mill 10` is provided with pressure rolls 12 and 14between which passes the material 16 being acted upon or processed inthe mill. In the particular illustration given, the material 16comprises a continuous strip which feeds off payolf reel 18 and iscoiled onto take-up reel 20. However, the direction of movement lof thestrip material through the mill 10 may be reversed, whereupon the reel20 will become the payoff reel and reel 18- will become the takeup reel.

Positioned on either side of the mill 10 are a pair of gage heads 19`and 21, each of which supports a vertically movable roller 22 positionedabove the strip as well as a, fixed roller 24 below the strip. Connectedto the vertically movable rollers 22 through linkages 25 and 26 areservo systems 28 and 30, respectively. Only the servo system 28,enclosed by broken lines, is shown in detail herein, it being understoodthat the other servo system 3d is identical in structure and operation.As the strip 16 passes through the gage head 19, for example, the gagingrollers 22 and 24 will be in rolling contact with its opposite surfaces;and as the thickness or gage of the material varies, the upper gagingroller 22 will move upwardly or downwardly, depending upon whether thestrip 16 increases or decreases in thickness. That is, when thethickness of the strip 16 increases, the gaging roller 22 and linkage 25will move upwardly; whereas, when the thickness of the sheet decreases,these members will move downwardly.

In order to sense the position of the gaging roller y22 and linkage v25,there is provided an electromechanical transducer, generally indicatedat 32, which produces an electrical output which varies in proportion tothe movement of roller 212. 'l'lhe transducer includes a center orprimary coil 3'4 which is connected to a source of alternating current36. At either end of the primary or center coil 34 and coaxial therewithare a pair of secondary coils 318 and 40. A rod-shaped magneticallypermeable core 42 is positioned axially inside the coil assembly andprovides a path for the magnetic flux ylinking the coils. Core 42 isconnected to the linkage 25 whereby the coil will be moved upwardly ordownwardly depending upon the direction of movement of the roller 22. Inseries with the primary winding 34 of transducer 32 is the primarywinding 44 of a second electromechanical transducer 46 which is similarin construction to transducer 32 and includes a pair of secondary coils48 and 50 as well as a movable, magnetically permeable core 52. In thiscase, however, the core 52 is connected through a mechanical linkage 54to a lever 56 which is controlled by means of a cam 58. The cam S8, inturn, is connected through gear reducer 6% to a two-phase servomotor 62having two phases or windings 64 and 66 included therein.

With reference to transducer 32, when the primary or center coil 34 isenergized with alternating current from source 36, voltages are inducedin the other two coils 38 and 40. These secondary coils are connected inseries opposition, meaning that the two voltages in the second- -arycircuit are opposite in phase whereby the net output of the transformeris the difference of the voltages. For one central position of the core,this output voltage will be zero. When the core 42 is moved from thiscentral position, the voltage induced in the coil toward which the coreis moved increases, while the voltage induced in the opposite coildecreases. This produces a ditferential voltage output which with properdesign varies linearly with a change in core position. T he motion ofthe core in the opposite direction beyond the central position producesa similar linear voltage characteristic, with the phase shifted 180.Operation of transducer 46 is identical to that of transducer 32. and,thus, by proper positioning of the cores 42 `and 52 in the respectivetransducers, the cumulative or output voltage produced across theirrespective secondary windings can be lmade equal and opposite in phase.These secondary windings are connected in series differential across theprimary winding 68 of an input transformer 78. Thus, when the outputvolta-ges produced across the secondary windings of the respectivetransducers are equal and opposite in phase, the voltage appearingacross the primary winding 68 will be zero. if the cores 42 and 52 areinitially positioned so that zero output voltage is produced acrosswinding 68, and if core 42 is thereafter moved upwardly, the outputvoltages produced across the secondary windings of the transducers willno longer balance, and a voltage will appear across winding `68. if thecore 42 moves downwardly from :a balanced condition7 then a voltage willagain appear across winding 68, but in this case it will be shifted inphase with respect to the voltage produced when it moved upwardly fromthe balanced condition. The voltages appearing across the secondaryWinding of transformer 78 are applied to an amplilier 72, the output ofwhich is connected across one of the windings 64 of the two-phaseservomotor 62. 'Tlhe other winding 66 of servornotor 62 is connected asshown to a source of alternating current voltage 74 which is in phasewith voltage source 36. In actual practice, the two voltage sources 36and 74 will probably be the same, but are shown herein separately forpurposes of explanation.

With the arrangement described, the servomotor 62 will rotate i-n onedirection or the other, depending upon the phase of the signal appliedthrough Winding 64. This phase will, in turn, depend upon the relativepositions of cores 42 and 52 in their respective transducers as wasexplained above.

The gear ratio of gear reducer 60 is on the order of twohundred to one,meaning that servomotor 62 will have to `make two-hundred revolutionsbefore the cam 58 rotates through 360. The arrangement is such that ifcore 42 in transducer 32 moves upwardly, for example, motor 62 willrotate the cam S8 to lower core 52 in transducer 46 until the voltagesat the secondaries of the transducers bal-ance and the servornotorstops. That is, as the core of transducer 32 is moved upwardly by roller22 in response to an increase in the thickness of strip 16, the couplingis increased between its primary winding 34 and secondary winding 38,and the voltage applied to the amservomotor 62 drives the core oftransducer 46 downwardly until the output voltages at the respectivesecondary windings are equal and the voltage appearing across winding 68of input transformer 70 is zero. At this point the motor stops, and what:has actually been done is to convert an electrical signal proportionalto the change in strip thickness into a proportional rotary motion ofthe servomotor 62.y That is, any change in thickness of the strip 16 asitpasses through the gage head will induce a proportional number ofrevolutions in the servomotor 62 until the two transducer outputs againbalance. If the thickness of the strip 16 decreases and the core 4Z.moves downwardly, the phase of the signal applied to the servomotor 62will y.be reversed, and the cam 58 will be rotated to lower the core 52in transducer 46.

The servomotor 62 is also connected through a mechanical connection 76to a binary digitizer, generally indicated at 78. The digitizer isessentially a rotary switching device 4for energizing particular relayswhich represent bits in a binary number. In the particular illustrationgiven, the digitizer 78 will produce an electrical signal comprisingeleven binary output bits which appear on leads 80. For a full andcomplete description of the digitizer, reference may be had tocope-riding application Serial No. 544, tiled January 5, 1960, now U.S.Patent 3,066,208 and assigned to the assignee of the presentapplication. Although the digitizerl shown in that application producesa decimal rather than a binary output, the conversion from decimal tobinary notation will be obvious to those skilled in the art. number A,for example, lwiil be represented by (A0, A1, A2, A3, etc.) where A0 isthe binary bit 20, A1 is the binary bit 21, A2 is the binary bit 22, A3is the binary bit 23, and so on. Each of the binary bits is representedon leads 80 by an ON or OFF signal, representing a one7 or zero,respectively in binary notation. Thus, if the output leads from thedigitizer 78 representing the A0 and A3 bits are ON or one while allother leads are OFF or Zero, it means that the output of the digitizeris 294-23, or l-{8 which is 9. Similarly, if only the A1 and A2 leadsare On or one While all other leads are OFF or zero, the signalrepresented is 214-22, or 2-l-4 which is 6. .Also included in the servosystem 28 is ap paratus, not shown, for automatically zeroing the systemwhen the two rollers 22 and 24 are in contact with each other. Thisapparatus forms no part of the present invention, but is fully shown anddescribed in the aforesaid U.S. Patent 3,056,208.

As shown in FIG. la, the sertvo system 30 is also connected through amechanical linkage 32 Ito a second,

digitizer `84 having eleven output leads 86. The corresponding outputleads from the digitizers 7S and 84 are each connected to a bit line,only one of said lines being shown in detail in FIG. lb and identifiedas bit line 0. Thus, the A0 leads from both digitizers 78 and 8d areconnected to bit line 0, the A1 leads from each digitizer Will beconnected to bit line l, the A2 leads from each digitizer will beconnected -to bit line 2, the: A3 leads from each digitizer will beconnected to bit line 3, and so on.

Included in the circuit is a mill drive direction selector 114 which,among other things, serves to control the to lead to disable or switchoff the digitizer 84. When, however, the direction of strip movement isreversed (i.e., from right to left in FIG. la) digitizer 78 will bedisabled while digitizer 84 is enabled to prod-uce binary bits on outputleads 86. Thus, only one set `of binary bits Y Thus, a binary fromdigitizer 7'8 or `84 will pass into the respective bit lines `-10.

All of the bit lines 1--10l are identical in construction to bit line 0shown in detail in FIG. lb. With reference to this rst bit line, itincludes an electron valve 11,2 having its grid 90 connected to the A0leads from each of the digitizers 78 and 84, it being understood thatonly one of these leads will be operative to pass ON signals at anytime, depending upon the direction of strip movement through the mill.The cathode 120 of valve 112 is connected through lead 122 to one end ofthe secondary Winding i124 of a transformer 126, the other end of thewinding 124 being connected through `a unidirectional current device 128to ground. The primary winding 130 of transformer 126 is connected to ablocking oscillator 132 which receives a trigger pulse from a gatecircuit 134, the arrangement being such that the output of the blockingoscillator will be a pulse each time a trigger pulse is received fromgate circuit 134, however the output pulse of the block-ing oscillatorwill be delayed with respect to Vthe input trigger pulse from circuit134. The delayed output pulse from the blocking oscillator is thencoupled through transformer 126 to lead 122 to thereby apply a negativepotential to the cathode 1120 and enable the electron valve 112 to passON signals from digitizer 78 or 84 as the case may be. At all othertimes, however, the valve 112 is disabled. Lead 122 is also connected tothe cathodes 120* in each of the remaining bit lines 1-1() where theaction is the vsame as that described with respect `to bit line 0.

The anode 136 of the tube 1112 is connected to a source of anodevoltage, designated B+, through the input 'winding 138 of a rst circularmagnetic core 140 in an entry gage memory unit 141 which serves to storeand `advance successive yactual entry gage measurements from valve 112in synchronous correlation with the movement of strip 16. That is, eachtime the valve 112 is enabled by blocking oscillator 132, it feeds theinstantaneous entry gage measurement in binary form from digitizer 78 or84 to the storage unit which progressively advances these instantaneousmeasurements from one end of the unit to the other end, the timerequired to advance from one end to the other being equal to the timerequired for the strip 16 to travel from the rollers 22 and 24 to thebite of the ymill 10.

Also included on the core 140 in the memory unit is a shift winding 142and an output winding i144 which is connected through diode 146 andresistor 148 to the input winding i138 of a second circular magneticcore 15d. As shown, a capacitor 152 is connected between the junction ofdiode 146 and resistor 1433 and the other end of the output winding 144.Core is identical to core 140 and includes an input winding 138, a shiftwinding 142 and an output Winding 144. Core 150, in turn, is coupled tocore 154 and this core, in turn, is connected to the next succeedingcore in the chain. in the particular embodiment of the invention shownherein, it will be assumed that there are ten such cores connected incascade, the last or 4tenth core being designated =by the numeral 156.

Each of the cores 140, 158, 154, etc. is formed from permanent magnetmaterial and may have flux remaining in either of two directionsdepending upon the last direction of the magnetizing current. In theillustration given, the input current in wind-ing 138 can cause llux toflow in core 140, for example, in a clockwise direction while theshiftcurrent in lwinding 142 can cause llux in the 'counterclockwisedirection. Current will flow 4in the output diode 146 only when the fluxchanges from clockwise to counterclockwise direction. Thus, a one or ONbit can be stored in the first core 148 by pasing current through theinput Winding 13'8. The one or ON bit can then be transferred to thesecond core by passing current through the shift winding 142. As shown,all of the shift windings 142 are connected in series to lead 158 which,in turn, is connected to the output of gate circuit 134. Consequently,all of the cores in the 'chain are shifted simultaneously. When a shiftpulse is applied to the shift windings 142, a one or ON bit in the firstcore 140, for example, will be transferred to the second core 1581. Asthe lluX changes, the diode 146 conducts and stores a charge in thecapacitor 152. Before the capacitor 152 can discharge, however, the core158 will have lalready received a shift pulse to transfer -itsinformation onto `core 154. Thus, when the capacitor 152 does discharge,the information which was stored on the rst core is transferred to thesecond core 151i by action of the capacitor 152 discharging through theinput winding 138 of this core. Information can ilow only one way due tothe diode and due to the ratio of turns between the input and outputwindings. Thus, the Icapacitors 152 act as a temporary sto-rage mediumwhile the cores are reset to Zero. lf there is no input current beforethe next shift current pulse, the lirst core rwill be in the zero statewith counterclockwise flux. Hence, the shift current cannot change theflux, no current will charge the capacitor, and the following core willremain reset, thus shifting the zero or OFF binary bit from the firstcore to the second core.

With the arrangement described, each bit will be transferred from onecore to the other until the final core 156 is reached. The outputwinding 144 of this core is then connected through lead 168 to aparallel binary sub- `tractor 162 which also receives the outputs fromthe other bit lines 1-l0. As the input gage of the strip materialvaries, this variation will be detected by the servo system 28 so thatthe output of digitizer 78, for example, will be constantly changing,assuming that the input gage is also changing. However, by virtue of thefact that the electron valve 112 conducts only at periodic intervals,samples of the input gage will be passed through bit lines O-lO atperiodic intervals also. As will hereinafter be explained, a sample ofthe input gage is passed to the cores 141), 150, 154, etc. each time thestrip 16 moves through six inches of travel. Since 4there are ten suchcores connected in cascade, the strip will have to travel sixty inchesor five feet before the output information arrives at the binarysubtractor 162. By positioning the rollers 22 and 24 tive feet from thebite of the mill, it will be appreciated that when the input gageinformation arrives at the subtractor 162, the increment of strip havingthat particular gage will be directly at the `bite of the mill.

#Reverting again to the rolling mill 10, input strip length (L1) is`sensed by equipment similar to that described iu copending applicationElongation Control System, Serial No. 680,349, filed August 26, 1957 andnow U.S, Patent 2,982,158, namely a pulse generator 164 and ademodulator unit 166. Similarly, output strip length (L2) is sensed by apulse generator 168 and demod-uliator unit `178. As shown, the outputsof the demodulators 166 and 170 are connected through switch means 172to leads 174 and 176. The switch means 172 is controlled by the milldrive direction selector 114, the 'arrangement being such that when the`strip 16 is vtravelling from left to right, the output of pulsegenerator 164 which represents input strip length (L1) is connected tolead 174, and the output of pulse generator 168 which represents outputstrip length (L2) is connected to lead 176. When, however, the directionof strip travel through the mill is reversed, the switch 172 willreverse the connections between the demodulato-rs 166 and 170 and theleads 174 and 176. That is, when the strip is travelling from right toleft, the output of pulse generator 168 will then represent input striplength (L1) so that ythe demodulator 178 will then be connected to lead174 rather `than lead 176. Similarly, under the conditions described,the output of pulse generator 164 will represent the output strip length(L2) so that the demodulator 166 will now be connected to lead 176rather than lead 174.

For purposes of explanation, it will be assumed that the strip istravelling from left to right so that the output of pulse generator `164is connected to lead 174 while the output of pulse generator 168 isco-nnected to lead 176. Connected to the lead 174 is another lead 178which applies the pulses or oscillations representing the input striplength (L1) to a rst L1 counter 180 which may, for example, be of theconventional Hip-flop type comprising a plurality of multivibratorsconnected in cascade. The counter 180 is preset whereby it will triggermultivibrator 182 to produce 1an output pulse whenever the counter 180reaches the count to which it was preset. In the illustration given, thecounter l18@ will be preset to trigger multivibrator 182 each time theinput strip moves through six inches. Thus, assuming that the gate 134is not disabled by a synchronizer 184, hereinafter described, a p-ulsefrom circuit 182 will pass through the gate y134 to the reset windings142 on cores 140, `1'50, etc. and also to the blocking oscillator 132.The output pulse from the blocking oscillator 132, however, will bedelayed with respect to that on lead 158 directly from gate 134, thearrangement being such that each of the `cores 140, 150, etc. will shiftthe information stored therein before new information is fed into thesystem from valve 112.

The pulses or 4oscillations on leads 174 and 1176 are also passed togate circuits 190 and 192, respectively. The output of gate circuit 190is then passed Ito a second L1 counter 194, the count of which is presetby means of a G22 preset circuit 196. The L1 counter 194, like counter180, may comprise any of the well known types having a series ofcascade-connected multivibrators. As is well known to those skilled inAthe art, ya counter of this type may be preset by a series `of switchclosures to count any desired number of oscillations before producing anoutput pulse. The circuit 7196, therefore, comprises a plurality ofswitches which may be closed to preset the counter 194 to count theydesired number of oscillations.

When the desired number of oscillations or pulses are counted by counter194, it will produce an output -to trigger the synchronizer 184 throughmultivibrator 198. A-t this point, the synchronizer will then disablethe gate 134 through lead 200 while enabling the parallel binarysubtractor circuit -162 through lead 282 to perform a binarysubtraction. At the same time, the synchronizer 184 will block gates19t) and 1192 through lead 204.

Revertin-g, now, to gate `192, its output is passed through lead 206 toan L2 counter 208 which will produce a binary output on ten leads 210which is proportional to the number of oscillations or pulses counted bythe L2 counter. The L2 counter is of the well-known type comprising aplurality o-f cascaded ip-ilop circuits and is reset to begin countingfrom zero by a signal from synchronizer 184 through lead 212. At thesame time the L2 counter 208 is reset, the L1 counter i194 is also resetby synchronizer `184 through lead 207, `substantially as shown.

It will be remembered that Aan error signal proportional to thedeviation in gage from a desired output gage is derived from theequation:

ri L1 in order to obtain the correct error signal.

The factor L ed is calculated as follows: It will be remembered that thesecond L1 counter 194 may be preset to count any nurn- 10 ber of pulsesor oscillations by `an appropriate number of switch closures in circuit196. By setting the switch closures so that the desired output gage G22is equal in magnitude to L1, the error equa-tion becomes:

ln other words, the L1 counter 194 is set to trigger multivibrator 198whenever L1 is equal to G2d. When this occurs, the synchronizer 184 isyactuated by the signal from multivibrator 198 to disable the gates 190and 192 through lead 204 whereby both the L1 counter 194 and the L2counter 288 stop counting. 'Ille output of the L2 Counter at thisinstant then represents the factor or the desired calculated input gageEl. At the same time, the synohronizer enables the subtractor 162 toperform a parallel binary subtraction of the calculated desired inputgage (El) from the actual input gage at the bite `of the mill (G1)toproduce Ia binary output error signal schematically illustrated by thelead 214.

While the subtract-ion process is being performed, the synchronizer 184blocks gate 134 so that no further information can pass through bitlines 0-10 during the subtraction process. After the subtraction processis then completed, the synchronizer will reset the L1 and L2 counters194 land 208 through leads 207 vand 212 and will enable the gates and192 to pass L1 and L2 pulses or oscillations to the counters to begin anew cycle. In this way, samples of the error signal (G1-@1) are obtainedat spaced points ialong the strip 16, `and the number of samples takenis dependent upon the preset value of G2d in switch closure circuit 196.That is, circuit 196 determines the number of oscillations (i.e., thelength of .the strip) required to produce the signal to trigger thesynohronizer 184; and this, in turn, depends upon the desired value ofG2d.

Operation of the system may possibly best be understood by reference toFIG. 2 where wave form A represents the yoscillations (L1) on lead 174.These oscillations, when fed to the first L1 counter 180 will cause themultivibrator 182 to produce an output pulse to gate 134 after every sixinches of strip travel. The pulses in Wave form B, then, are those whichare passed through wind-V ings 142 in the cores 140, 150, etc. to shitthe cores and advance the information through the memory unit each timethe strip travels six inches. The output `ot the blocking yoscillator132, on the `other hand, is represented by wave form C in FIG. 2 Wherethe pulses have the same frequency as those in w'ave form B but aredelayed with respect to the pulses in wave form B. Thus, Aas wasmentioned above, the cores are first shifted to advance infor- `mationto the memory unit, followed by the introduction of new information intothe unit `from valve 112.

During the time that wave forms B `and C are being generated, the waveform A is lfed also to the second L1 counter 194 which is preset bycircuit 196.. After the L1 counter 194 has counted #a predeterminednumber of pulses yor oscillations in wave form A determined by thesetting sof circuit 196, it will trigger multivibrator 198 to produce an`output pulse 209 wave form D of FIG. 2. The pulse 209 in wave form Dthen actuates the synchronizer 184 to produce the pulse 211 in wave formE on lead 202 which enables the binary subtractor circuit 162 to performa subtraction operation between times T1 and T2. At time T2, a pulse 213is produced in Wave form F, -and this pulse `is fed through leads i207.and 212 to the L1 `and L2 counters to reset them whereby they againstar-t `counting from zero, the pulse in wave form F persisting betweentimes T2 `and T3. Wave form G from the synohronizer 184 is ted throughleads 200 and 204 to gates 134, 190 and 192. This wave form includes apulse 215 which starts at time T1 :and persists for a short time afterT2, thereby disabling the gates 134, 190 and 192 yand prevent-ing theleed-in of information :to the cores 140, 150, 154, etc. as well as thecounters 194 and 208 during the period of subtraction.

The output of the binary subtrractor 162 on lead 214 is a :binary signal`having ra magnitude proportional to the difference between the yactualmeasured input gage (G1) and fthe calculated desired input gage (61).This signal is passed through a dead zone and yalarm set circuit 216 and:a time control cincuit 218 to the mill screwdoivn conrtrol 220. lf theoutput of ythe subtractor 1612 indicates ithat Ithe gage is above G2d,`a signal will be fed on lead 222 to the mill screw control 1224 tolower the upper rol 12. Similarly, if the output of the subtractor 162indicates that the `gage is below G2d, a signal will be fed on lead 226to the screw control 224 to raise the roll 12. Also connected to themill screwdown control circuit 226 are two alarms 2281and 230. Alarm 228be actua-ted to 4signal the ropenator that the error signal is above apredetermined magnitude while 230 will -signal the operator mhat ftheerror signal is below a predetermined magnitude. In this manner, whenthe mill initially starts up `and [the G1 information fed through thestorage circuit of cores 140, 148, etc. is obviously incorrect, since itwas derived from strip prewiously rolled, the operator' will be.apprised of this `fact by one of `the alarms 228 or 239. Included inthe system is switching means, not shown, enabling the operator to placethe screw control 224 on either manual or automatic operation wlrereinthe output of the subtraotor 162 controls. enables the operator to4control the mill by manual means until the alarm ceases, indicatingthat the correct G1 information has arrived at the outputs of bit linesO-l 0.

The invention thus provides ra mill screvvdown control based on theconstant volume principle which derives an error signal by comparison ofactual input gage of the material at the bite of the mill withcalculated desired input gage, 'and wherein fthe latter lfactor isderived in Ian electrical computer from `a consideration of the factorsL1, L2 and G2d only while ignoring any other factors such as the W and K:factors employed in previous systems of this type. At the same time,contrary to what might be expected, a uniform output gage is derived,notwithstanding the fact that the aforesaid liactors are eliminated.

Although lthe invention has been shown in connection with a certainspeciic embodiment, it will be readily apparent to those skilled in thefart that various changes in form rand arrangement of parts may be made-to suit requirements without departing from the spirit and scope of theinvention. IIn this respect, it will be apparent that the binary errorsignal G1-'G`1 derived from the subtrac- .tor 162 may -be used to varythe .tension in strip 16 rather than the screw control 224 with the sameoverall effect (i.e., ta constant and uniform output gage).

We claim as our invention:

l. In an electrical control system for a mill gage varying device basedupon the principle of constant volume of material entering and leavingthe mill and wherein the deviation from a desired output gage of thematerial is represented by an electrical signal proportional to where G1is the actual gage of the material entering the bite of the mill, L2 isthe actual length of the material leaving the mill for a given volumeentering the mill, L1 is the actual length of the material entering themill for said given volume, and G2C1 is the desired output gage of thematerial leaving the mill; the combination of an actual gage measuringdevice for deriving an electrical signal which varies as a function, ofG1, a Erst pulse generator for generating a number of pulsesproportional to L1, a second pulse generator for generating a number oipulses proportional to L2, a lirst counter for counting the pulses fromsaid lrst pulse generator, a second counter for counting the pulses fromthe second pulse generator and adapted to produce an output signal whichvaries as a function of L2, means for presetting said rst counter toproduce an output signal when vthe number of pulses counted by saidfirst counter is equal in magnitude to Ggd, and apparatus operable inresponse to the output signal from said first counter for electricallysubtracting the output signal from said actual gage measuring device andthe signal from said second counter to produce an error signal forcontrolling said mill gage varying device.

2. In an electrical control system for a mill gage varying device basedupon the principle of constant volume of material entering and leavingthe mill and wherein the deviation from a desired output gage of thematerial is represented by an electrical signal proportional to where G1is the actual gage of the material entering the bite of the mill, L2 isthe actual length of the material leaving the mill for a given volumeentering the mill, L1 is the actual length of the material entering themill for said given volume, and G2d is the desired output gage of thematerial leaving the mill; the combination of an actual gage measuringdevice for deriving a binary electrical signal comprising a plurality ofbits which together represent the quantity G1, a rst pulse generator'for generating a number of pulses proportional to L1, a second pulsegenerator for generating a number of pulses proportional to L2, a firstcounter for counting the pulses from said tirst pulse generator, asecond counter for counting the pulses from the second pulse generatorand adapted to produce a binary electrical output signal comprising aplurality of binary bits which represent the quantity L2, means forpresetting said rst counter to produce an output signal when the numberof pulses counted by said rst counter is equal in magnitude to G2d, andbinary subtractor apparatus operable in response to the output signalfrom said rst counter for electrically subtracting the binary signalfrom said actual gage measuring device and the signal from said secondcounter to produce an error signal for controlling said mill gagevarying device.

3. In an electrical gage control system for a mill screw- Vdown basedupon the principle of constant volume of material entering and leavingthe mill and wherein the deviation from a desired output gage of thematerial is represented by an electrical signal proportional to where G1is the actual gage of the material entering the bite of the mill, L2 isthe actual length of the material leaving the mill for a given volumeentering the mill, L1 is the actual length ofthe material entering themill for said given volume, and G2d is the desired output gage of thematerial leaving the mill; the combination of a device for deriving anelectrical signal which varies as a function of G1, a rst pulsegenerator for generating a number of pulses proportional to L1, a secondpulse generator for generating a number of pulses proportional to L2, afirst counter for counting the pulses from said first pulse generator, asecond counter for counting the pulses from the second pulse generatorand adapted to produce an output signal which varies as a function ofL2, means for presetting said rst counter to produce an output signalwhen the number of pulses counted by said rirst counter is equal inmagnitude to G2d, apparatus adapted to electrically subtract the outputsignal from said device and the signal from said second counter toproduce an error signal for controlling said mill screwdown, andsynchronizing means responsive to the output signal from said firstcounter for enabling said subtracting apparatus to perform a subtractionoperation while at the same time stopping said tiist second countersduring the subtraction process.

4. ln an electrical control system for a mill screwdotvn based upon theprinciple or" constant volume or" material entering and leaving the milland wherein the deviation from a desired output gage of the materialrepresented cy an electrical signal proportional to L2 Cir-EGM where G1is the actual gage of the material entering the bite or the mill, L2 isthe actual length of the material leaving the for a given volumeentering the mill, L1 is the actual length of the material entering themill for said given volume, and Gm is the desired output gage of thematerial leaving the mill; the c bination oi an actual gage measuringdevice for deriving an electrical signal which varies as a function or"G1, a iirst puise generator for generating a number of pulsesproportional to L1, a second pulse generator for generating a number orpulses proportional to L2, a rst count-er for c unting the pulses fromsaid first pulse generator, a second counter for counting the pulsesfrom the second pulse generator and adapted to produce an output signalwhich varies as a function of Lg, gate circuits connecting the lirst andecond pulse generators to the first and second counters, respectively,means for presetting said lirst counter to produce an output signal whenthe number or pulses counted by said rst counter is equal in magnitudeto Gza, apparatus adapted to electrically subtract the output signalfrom said actual gage measuring device and the signal from said secondcounter to produce an rror signal for controlling said mill screv'doufn,synchronizing means responsive to the output from said first counter forproducing a gating pulse to disable said gate circuits while at the timeenabling said subtracting apparatus to perform a subtr -ctiou operationand thereafter reset said second counter to begin counting from zerobefore the gating pulse is removed iron the gate circuits to enable thesame to pass pulses to the l rst and second counters.

5. A system based on the constant volume principle for automaticallycontrolling the operation of a mill gage varying device to produce auniform desired output gage in strip material passing through the millcomprising, in combination, means for measuring the actual input gage ofstrip material entering the mill, an entry gage memory unit, said entrygage memory unit containing stored material entry gage measurementsirorn said means for measuring the actual input gage of the stripmaterial entering the mill, means for adr/ancinf' material entry gagemeasurements through said entry gage memory unit in synchronouscorrelation with the advancement of strip ruaterial through the mill,means in said automatic control system for measuring the actual inputlength of material entering the mill, means in said automatic controlsyste for measuring the actual output length or material leaving themill, means for inserting desired output gage measurement of the stripmaterial into said automatic control system, means in the automaticcontrol system for computing the calculated desired output gage of stripmaterial leaving the mill from a consideration oi the actual length ofthe strip material entering the mill, the actual length of stripmaterial leaving the mill and said inserted desired output measurement,and means for producing an error signal to control said mill gagevarying device by comparison of said calculated desired material entrygage and said actual material entry gage measurements which have beenadvanced through said entry gage memory `6. in a system for controllinga mill based on the principle of constant volume or" material enteringand leaving the mill, the combination of 'lirst means for producing anlectrical signal which varies as a function of the length or stripmaterial entering the mill, second means for producing an electricalsignal which varies as a function of the length of strip materialleaving the mill, third means rlor producing an electrical signalproportional in magnitude to the desired output gage of strip 1r 'elleaving the rolling rnill, and computer apparatus responsive to onlythose electrical signals produced by said rst, second and third meansfor calculating the desired input gage of strip material entering themill.

7. ln a system for controlling a mill based on the principle of constantvolume of material entering and leaving the mill, the combination offirst means for producing an electrical sigr which varies as a functionof the length of strip material entering the rolling mill, second meansfor producing an electrical signal which varies as a fund tion ot thelength ol strip material leaving the rolling Aiill, t'nird means forproducing am electrical signal proportional in magnitude to the desiredoutput gage of strip material leavin the rolling mill, computer'apparatus responsive to only the el ctrical signals produced by saidfirst, second and third means for calculating the desired input gage ofstrip material entering the mill and for producing an output signalwhich varies as a function o said calculated desired input gage, fourthmeans for producing an electrical signal which varies as a function ofthe actual input gage of strip material entering the bite of the mill,and apparatus responsive to the signals from said `fourth means saidcomputing apparatus to derive an electrical signal for controlling saidrolling mill screwdown.

8. ln a system for controlling a mill in accordance with the principleof constant volume of material entering and leaving the mill bycomparison of actual measured material entry gage and calculated desiredmaterial entry gage; the improvement of means including electricalcomputer' apparatus for deriving calculated desired material entry bycomparison of only the three actors of actual input length of materialentering the mill, actual output length of material leaving the mill,and selected desired output gage.

References Cited in the tile of this patent UNlTED STATES PATENTS2,982,158 Orbom May 2, 1961 3,015,974 Orborn et al Jan. 9, 19623,054,311 Murtland Sept. 18, 1962 OTHER REFERENCES Flat Rolled Products,pages 7-9, lan. 2l, 1959. (Copy in Div. 13, TS-340m4-c.2.)

8. IN A SYSTEM FOR CONTROLLING A MILL IN ACCORDANCE WITH THE PRINCIPLEOF CONSTANT VOLUME OF MATERIAL ENTERING AND LEAVING THE MILL BYCOMPARISON OF ACTUAL MEASURED MATERIAL ENTRY GAGE AND CALCULATED DESIREDMATERIAL ENTRY GAGE; THE IMPROVEMENT OF MEANS INCLUDING ELECTRICALCOMPUTER APPARATUS FOR DERIVING CALCULATED DESIRED MATERIAL ENTRY GAGEBY COMPARISON OF ONLY THE THREE FACTORS OF ACTUAL INPUT LENGTH OFMATERIAL ENTERING THE MILL, ACTUAL OUTPUT LENGTH OF MATERIAL LEAVING THEMILL, AND SELECTED DESIRED OUTPUT GAGE.